Modulations of ν_O–H and ν_C═O Stretching Frequencies of Difluoroacetic Acid with Internal Rotation of CHF₂ Rotor: A Combined Vapor Phase and Matrix Isolation Infrared Spectroscopy Study

Abstract

Mid-infrared spectra of difluoroacetic acid (DFAA) have been measured by isolating the molecule in argon and nitrogen matrices at 8 K and also in the vapor phase at room temperature. In argon matrix, the O–H stretching fundamental (νO–H) of −COOH group appears as a doublet with band maxima at 3554 and 3558 cm–1, and a similar doublet for CO stretching fundamental appears at 1800 and 1810 cm–1. In the vapor phase, the νO–H transition is featured with multiple peaks, and the observed band shape has been deconvoluted as superposition of two transitions both having A-type rotational band contours. We have attributed these transitions to the two internal rotational isomers corresponding to the two distinct minima along −CHF2 torsional coordinate of the molecule. Natural bond orbital (NBO) analysis reveals that these torsional minima are the manifestations of different second order interactions involving bonding and antibonding orbitals corresponding to the rotor −CHF2 and COOH groups of the molecule. By use of the theoretically predicted rotational constants of the rotamers, the band profile for νO–H has been simulated satisfactorily by means of the PGOPHER method, and this has allowed estimating accurately the energy difference between the two rotamers as 0.54 kcal/mol. The predicted energy barrier for interconversion between the rotamers is very small, ∼0.5 kcal/mol from rotamer II to rotamer I, which implies that the molecule could hop almost freely between the two rotameric forms at room temperature. As a result, the frequencies of the key stretching vibrational modes, like νO–H, νCO, and νC–H, undergo modulation with internal rotation of the rotor −CHF2 group. Such modulation of high frequency modes could be an efficient mechanism for acceleration of rotor-induced IVR (intramolecular vibrational redistribution) well documented in the literature. Furthermore, the spectra measured in matrix isolated environment show signatures for an energetically higher third rotamer, where −OH and −CO groups are in anti orientation. It has also been shown that DFAA can easily form weak hydrogen bonded dimeric complexes with molecular nitrogen (N2), which causes νO–H to undergo a red shift of ∼30 cm–1 in argon matrix for all three DFAA monomers.

Biosorption of cationic Hg2+ and Remazol brilliant blue anionic dye from binary solution using Gelidium corneum biomass

“…The FTIR spectrum of the Gelidium corneum biomass before the bio-adsorption process of Remazol brilliant blue dye and Hg 2+ revealed absorption bands characterized for various functional groups. Consequently, an absorption band at ν = 4069 cm −1 was identified for –OH hydroxyl group stretching as indicated by Bhattacharya et al 71 . Li et al 72 established the absorption band at ν = 3442 cm −1 for –OH or N–H stretching vibration band.…”

“…(cm −1 ) Annotations Wave no. (cm −1 ) Annotations 4069 –OH hydroxyl groups stretching 4056 –OH hydroxyl groups stretching “alcohol” 13 Bhattacharya et al 71 3442 –OH or N–H stretching 3597, 3578, 3557 Strong broad –OH stretching − 155 Li et al 72 2934 C–H stretching of aliphatic hydrogens or OH stretching 2940 Medium C–H stretching “alkane” − 6 Zhao et al 73 2349 Carbon dioxide or Si–C stretching 2351 Carbon dioxide or Si–C stretching − 2 – 2250 Weak S–H stretching “thiol” 2239 Weak C≡N stretching “nitrile” or weak C≡C stretching “alkyne” 11 Samson & Otaraku Ipeghan 74 2169 Strong S–C≡N stretching “thiocyanate” 2167 Strong S–C≡N stretching “thiocyanate” 2 Dujearic-Stephane et al 75 1642 C=O amidic carbonyl or strong C=C stretching 1665 C=O, Carbonyl group “ketonic carbonyl” “conjugated ketone” − 23 Di et al 76 1542 C=C stretching or Amide–II (protein N–H bend, C–N stretch) 1547 Strong N–O stretching “nitro compound” …”

Medium-Dependent Crossover from the Red to Blue Shift of the Donor’s Stretching Fundamental in the Binary Hydrogen-Bonded Complexes of CDCl3 with Ethers and Ketones

“…Purities of all of the compounds were checked before use by recording the electronic absorption and Fourier transform infrared (FTIR) spectra of very thin films of the chemicals as supplied. The apparatus used to record the matrix isolation infrared spectra of CDCl 3 and its binary complexes has been described elsewhere. , In brief, argon gas (purity 99.9%) was mixed in large excess with sample vapor in a stainless steel chamber, and the final vapor mixture was deposited through an effusive nozzle of diameter ∼500 μm onto a cold and polished KBr window maintained at ∼8 K. The KBr window was mounted on the cold finger of a closed-cycle helium refrigerator (Advanced Research Systems, Inc., model no. DE202).…”

Efficient and Stable Perovskite Solar Cells by Fluorinated Ionic Liquid–Induced Component Interaction

“…[ 21 ] The peaks at 1105 and 1050 cm −1 are for ν CF, 1670 cm −1 is for ν CO, and 1528 cm −1 is for νCO, which are the characteristics of the anion CF 2 HCOO − as reported in literature. [ 22 ] Furthermore, Liquid‐state proton nuclear magnetic resonance ( 1 H NMR) is conducted for the confirmation of the existing of CH 3 NH 3 + and F 2 CH + in MA + DFA − , as shown in Figure S1, Supporting Information. The thermal stability of MA + DFA − is characterized by thermogravimetric analysis (TGA), as shown Figure 1c.…”